Etching of enamel surfaces: Improvements in etching procedures will be sought which will reduce the loss of mineral. Special emphasis will be placed on procedures for incorporating fluoride into the tooth in the form of fluorapatite. Topical fluoridation procedures: Further studies will be carried out to improve procedures which involve formation of CaHPO4.2H2O in the tooth by a pretreatment, followed by a fluoride solution which converts the CaHPO4.2H2O into fluorapatite. Emphasis will be placed on testing of new modalities of application. Animal studies will continue and preliminary clinical studies will be initiated. Mechanism of fluoride cariostasis: Improvements will be made in the diffusion cell used to study the dynamics of diffusion so that steady state will be attained more rapidly. The effects of neutral salts on the composition of the solution within the "caries" compartment will be studied. Role of octacalcium phosphate in tooth formation: Radioactive phosphorus will be used in an effort to study the involvement of octacalcium phosphate in enamel mineral formation.